1. Field of Invention
The present invention relates to a stacked-die package structure. More particularly, the present invention relates to a stacked-die package with a ball grid array (BGA) structure.
2. Description of Related Art
Integrated circuits (ICs) significantly influence on every aspect of human""s life and have a variety of applications for various fields. In modern era, all products trend towards more small and light for convenient purposes. Accordingly, the ICs also become smaller than ever. Current semiconductor technology is heading towards a 0.18-micron process. For the IC products, three stages are usually required: fabricating silicon wafers, manufacturing IC circuits and packaging the IC dies. Namely, the package is the finally stage for completing the IC products. The package can be provided as a medium for electrically connecting between dies in the package and the printed circuit board (PCB), or between the dies and other elements. In addition, the package can protect the dies therein from damage as well.
FIG. 1 shows a conventional structure of a stacked-die package. Generally, a ball grid array (BGA) structure is usually used for a stacked-die structure. For example, similar memory dies can be packed within one package for increase memory capacity. As shown in FIG. 1, a first die 106 is attached to a substrate 102 first, and then a second die 108 is stacked on the first die 106. Adhesive layers 104 are formed between the substrate 102 and the first die 106, and between the first die 106 and the second die 108. Then, a wire bonding process is performed for electrically connecting the first die 106 to the substrate 102 using conductive lines 110a, and for electrically connecting the second die 108 to the substrate 102 using conductive lines 110b. A mold compound 114 is formed over the substrate 102 to encapsulate the substrate 102, the dies 106, 108, and the conductive lines 110a, 110b. Finally, solder balls 112 are assembled to the back surface of the substrate 102.
However, the structure above requires that the first die 106 must larger than the second die 108, or that a width difference for each side of the two dies 106, 108 must be greater than 0.3 mm. If the two dies 106, 108 have the same sizes, the wire bonding process will fail, or the second die will short the conductive lines 110a. 
FIG. 2 shows a top view of a conventional stacked-die structure. A first die 806 is sat on a substrate 802, and a second die 808 is then stacked on the first die 806, in which the first die 806 and the second die 808 are perpendicular to each other. There are several bonding pads on the two sides of each die 806, 808. For preventing crack or collapse of the second die 808 during wire bonding, spacers 840 are formed under two other sides of the second die 808 for shoring the second die 808. However, the conventional stacked-die structure is not suitable for dies having bonding pads located on their four peripheral sides.
FIG. 3 shows a conventional structure of a stacked-die package using a lead frame as a carrier. The structure shown in FIG. 3 is issued to U.S. Pat. No. 5,291,061. A first die 906 and a second die 908 have almost the same sizes. The first die 906 is affixed to the lead frame 902, and conductive lines 910a are electrically connected the first die 906 to the lead frame 902. A polyimide tape 930 is attached on the first die 906, and then the second die 908 is stacked on the polyimide tape 930. Conductive lines 910b are then electrically connected the second die 908 to the lead frame 902. Finally, a mold compound 914 is used for encapsulating the first and second dies 906, 908, the conductive lines 910a, 910b and the lead frame 902, while pins 932 of the lead frame 902 are exposed. In the prior art structure, the polyimide tape 930 costs high and its thermal conductivity is bad, causing that the second die 908 is not easily to dissipate heat. Furthermore, it requires special tapping machine for taping the polyimide tape 930 between the dies 906, 908 under a high temperature condition above 400xc2x0 C., thus increasing cost. In addition, the polyimide tape causes the cushion effect on the second die 908, affecting the quality and reliability of wire bonding for the second die 908.
The present invention provides a stacked-die package structure capable of stacking dies having substantially the same size and bonding pads around the peripheral sides of the dies within one package.
The present invention provides a stacked-die package structure for reducing the cushion effect, which usually occurs in the conventional stacked-die structure.
The present invention provides a stacked-die package structure capable of increasing efficiency of heat dissipation.
The present invention provides a stacked-die package structure for reducing cost and simplifying manufacturing process.
As embodied and broadly described herein, the invention provides a stacked-die package structure. A carrier having an upper surface and a back surface opposite to the upper surface is provided. A number of dies are stacked one by one on the upper surface of the carrier, and a number of bonding pads formed around the peripheral sides of each die. A number of spacers are located between two adjacent dies. Adhesive layers are located between the spacers, the dies, and the carrier for adhering layers therebetween. Conducting lines are used for respectively electrically connecting each of the bonding pads of the dies and the carrier. And, a mold compound is formed over the upper surface of the carrier, for encapsulating the spacers, the dies and the adhesive layers.
The invention also provides a stacked-die package structure. A carrier having an upper surface and a back surface opposite to the upper surface is provided. A number of dies are stacked one by one on the upper surface of the carrier, and a number of bonding pads are formed around the peripheral sides of each die. Spacers are located between two adjacent dies, and one of the spacers, which is located on a top of the stacked dies, has a thermal dissipation surface. Adhesive layers are located between the spacers, the dies, and the carrier for adhering layers therebetween. Conducting lines are used for respectively electrically connecting each of the bonding pads of the dies and the carrier. And a mold compound is formed over the upper surface of the carrier, for encapsulating the spacers, the dies and the adhesive layers, but the heat dissipation surface is exposed.
The invention further provides a stacked-die package structure. A carrier having an upper surface and a back surface opposite to the upper surface is provided. A number of dies are stacked one by one on the upper surface of the carrier, and a number of bonding pads are located around the peripheral sides of each die. A thermal dissipation plate is stacked on the dies, having at least one thermal dissipation surface. A number of spacers are located between two adjacent dies, and between the dies and the thermal dissipation plate. Adhesive layers are located between the spacers, the dies, the thermal dissipation plate and the carrier for adhering layers therebetween. Conducting lines are used for respectively electrically connecting each of the bonding pads of the dies and the carrier. And, a mold compound is formed over the upper surface of the carrier, for encapsulating the spacers, the dies and the adhesive layers, but the heat dissipation surface of thermal dissipation plate is exposed.
Advantageously, the material of the adhesive layers can be silver paste, or paste with thermal conductivity and non-electrical conductivity, such that the adhesive process is not necessary to be performed under a high temperature above 400xc2x0 C., simplifying the manufacturing process and avoiding crack or collapse of the first and the second dies during the adhesive process under high temperature. It can also avoid cushion effect due to the insufficient rigidity of the second die when the wire bonding process for the conductive lines is performed using supersonic, and therefore increases the yields. Moreover, the material of the spacers has good thermal conductivity and its thermal expansion coefficient is approximate to that of the dies so that the thermal stress is reduced. By exposing the surface of the spacer or adding a thermal dissipation plate for increasing heat dissipation surface, the thermal dissipation efficiency further increases.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.